The function “hold gear” with automatic transmissions in drive trains of motor vehicles is already known. Hereby, when in automatic transmission mode, an actually intended gear change is prevented and a currently used gear, or selected gear, respectively, will be maintained. To meet a driver's intended selection, the function can be activated, in principle, through a control device and analysis algorithms, either automatically or manually through a direct request from the driver.
Known control systems with automatic activation of the function use the temporary retention of a gear as part of the transmission control program, for example, to arrange for an individual style of driving, like a mainly sporty or mainly economical driving style. DE 197 33 464 B4 and DE 43 25 296 A1 can be mentioned as examples. Hereby, the function “hold gear” will automatically be activated or deactivated. Although these methods can recognize a driver specific handling, they are, however, limited in reacting to changing drive situations and in anticipating the driver's observations while driving, and to initiate, based on a current situation, the function “hold gear”.
In the function “hold gear”, requested and initiated by the driver, below used as term “Hold Current Gear” or simply as hold gear function, the driver is given the option, to stop directly automatically initiated or computed gear shifting by the transmission control, meaning to keep a currently selected gear, as opposed to change the gear, as arranged by the transmission control.
The background here is that, due to the driver's observations, knowledge of specific road conditions or other secondary factors can be obtained, which would not require a gear shifting, or which might be disadvantageous to the actual operating condition, respectively. It can happen, for example, when going uphill, downhill, during stop and go traffic, in rough terrain, or when maneuvering.
The driver can usually signal the request “hold current gear” to the transmission control, in the typical manner through an operator's control element. Control elements, which display the particular gear condition directly through, for example, a snap-in key at the drive switch, or indirectly through a display, the function can remain active as long as the vehicle, or the drive train respectively, work within an allowed operating range, or what the control element displays, respectively. It is then up to the driver, by activating the switch, to terminate the function at a given time. With switches, which activate the hold gear function but do not explicitly display the function, for example a non snap-in key switch, an obligatory feedback operation is provided in the transmission control, through which the hold gear function is terminated.
In most cases, it will be bothersome to the driver to deactivate the selected function through the operator's control element, after the reason for the selection of an activation disappears, at the latest after a request through a display when changing the gear's allowed range, and again the need for the activation of the control key, or to unlock the snap-in key, respectively. It addition, this might be unnecessarily distractive in regard to the actual driving situation. In other situations, it might be absolutely necessary to have the transmission control to intervene and to terminate the hold gear function, to guarantee a regular drive condition, or to exclude an excessive wear, or in the extreme to avoid damage to the transmission, or other damage to the drive train, respectively. Therefore and in principle, it is more comfortable and suitable to provide a feedback operation, when terminating a hold gear condition and returning to the automatic transmission mode of the transmission control software.
It is known to prearrange the return to the automatic drive operation, chronologically after passing a fixed time span. This very simple criterion does not always make sense or is sufficient, since the request to return to the automatic drive condition can already be made, for instance, when the vehicle is standing still and while waiting a certain time period for starting the vehicle. Examples here are the stop at a traffic light or an intersection, or the boarding or release of passengers at a bus stop. In these cases, the time limitation of the function would at least partially pass, or going nowhere, respectively, without the vehicle being in the particular and expected drive situation, which was initiated by the hold gear request. Such a situation, where the hold gear request was performed, can be, as an example, an uphill slope lying ahead. A similar situation would occur during a stop-and-go drive at a slope; the function could be terminated before the slope would have been passed. Therefore, the use of a fixed time interval is rather imperfect as a return condition.